Safecast Seaweed Collection Feasibility Study

It is known that much of the radiation from the Fukushima incident — about 80% — went into the ocean, and while this would appear to be good for land dwellers, what is not known for certain is how much of that radiation is making its way into the food chain. Seaweed, which is consumed by people as well as some of the creatures that people eat, would appear to be a good place to look for concentrations of radiation.  Marco Kaltofen of Worcester Polytechnic Institute kindly offered to run a range of tests on any seaweed samples we sent him.

Map description: The red markers indicate stops were made with no sample collected, green, samples were collected. Mousing over (or clicking) on the markers will bring up a short description and picture(s).
Collection Location Map link

Although seaweed is usually collected by boat, Safecasters Jonathan Wilder and Jeremy Hedley drove north from Tokyo to Fukushima over the 2014 Spring Equinox weekend to collect as many samples as possible from shore, whether they were growing on rocks, washed up on the beach, or being sold as food in souvenir shops. Their brief was to find out whether valid samples for a Safecast project aiming to test for radioactivity in seaweed collected at one kilometer intervals, 200 kilometers north and south of the Dai-ichi nuclear plant, could be collected efficiently from land.


Much of the coast was under reconstruction. Seaweed could be seen at many locations but was mostly inaccessible due to a high tide early on the collection day, high waves the entire day, and physical barriers to the water.


The first location seaweed could be collected required a 1.5-meter jump down to the slippery tetrapods. It was tricky collection work with one hand both scraping the sea lettuce off and scooping it into the bag which was held in the other hand….


…before a wave washed the scrapings away.


We saw very little seaweed washed up on shore. This amount, washed up and collected from about a 50-meter stretch of beach, was nowhere near the 280 grams of wet seaweed needed for a single sample and was abandoned.


At a brand new port, so new that no boats were tied up yet…


…we thought we had found a great sample floating in the water.

One option was for one of us to jump into the water to retrieve it, but from this spot there was no way back out except for a long, forbidding swim in cold turbulent waters around to a ladder.

We wished we had brought a wetsuit and fins or a gaff, which we had imagined would be useful before we left on this expedition, or long secateurs, pruning shears. Lacking those, but in true Safecast spirit, we then looked around the port to see what we could scrounge to help with snagging the seaweed. We didn’t have much hope of finding anything, because the port area was clean; there were no nets, traps, gaffs, the things that one might expect to see lying around. Nothing was there except a pair of old boots and… a long bamboo pole (top left corner) with a long piece of string attached at one end and weighted with a piece of rebar on the other. To us, at the moment of realizing what we had found, it was unbelievable there would be a device lying around that could be exactly the thing that would work… Unfortunately, the seaweed was too securely rooted to the bottom to be pulled up.


Near the end of our first day of collection, after many mostly fruitless stops, we were treated to some classic Japanese scenery (not to say that the scenery had been unimpressive all day long), however, like many places that day, the seaweed was inaccessible. It was prohibited to cross the bridge to the island most likely because the railing (right) which had been destroyed by the March 2011 tsunami had yet to be repaired. Nonetheless, the bridge was crossed, seaweed was visible, but high seas again prevented collection.


On day two, the weather was pristine and the waters calmer. (Still, seawall construction was evident.) Seaweed could not be collected from this location.


Seaweed collection was relatively easy from this location with only occasional waves washing over the half-buried tetrapod.


From this boat ramp, two samples were collected, one growing at the far end and the other scattered about on the boat ramp, possibly washed in from a seaweed farm.


By the end of the two days, 10 samples were collected from 16% of the stops. They were then dried and shipped to Marco Kaltofen for testing. Preliminary results: “Samples were evenly split between low (single digit Bq/kg) and not detected.”  We’ll update this blog post when the entire series of tests is complete.

As for the feasibility of shore collection, even during a different season, or without heavy seas, it was concluded that collection could be more efficiently accomplished by boat.

by Jonathan Wilder


The full report

Feasibility Study — Seaweed sample collection Protocol

Sample Tracker

Collection Environment


About the Author

Azby Brown

Azby Brown is Safecast's lead researcher and primary author of the Safecast Report. A widely published authority in the fields of design, architecture, and the environment, he has lived in Japan for over 30 years, and founded the KIT Future Design Institute in 2003. He joined Safecast in mid-2011, and frequently represents the group at international expert conferences.